1. Field of the Invention
The present invention relates to an intake air amount control system for an engine, including a plurality of throttle devices each of which comprises a butterfly-type throttle valve rotatably carried in an intake passage body defining an intake passage for controlling the opening degree of the intake passage, the throttle devices being disposed in a pair at each of two points spaced from each other in a direction perpendicular to rotational axes of the throttle valves, the intake passage bodies of the throttle devices disposed at the two points being connected to each other by at least one connecting member.
2. Description of the Related Art
Such intake air amount control system is conventionally known, for example, from Japanese Patent Application Laid-open No. 10-176637 and the like, and designed such that the throttle valves of the pair of throttle devices are driven in operative association with each other by an interlocking mechanism.
In the above intake air amount control system, the pair of throttle valves are operated in association with each other so that they are opened slightly upon starting of the engine. Thus, the opening degree of each of the throttle valves is small and for this reason, there is a possibility that the amount of air at the start of the engine may be unstable, whereby the idling rotational speed of the engine becomes unstable.
Accordingly, it is an object of the present invention to provide an intake air amount control system including a plurality of throttle devices, wherein the idling rotational speed of an engine can be stabilized, while avoiding an increase in size of the intake air amount control system.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an intake air amount control system for an engine, comprising a plurality of throttle devices each of which comprises a butterfly-type throttle valve rotatably carried in an intake passage body defining an intake passage for controlling the opening degree of the intake passage, the throttle devices being disposed in a pair at each of two points spaced from each other in a direction perpendicular to rotational axes of the throttle valves, the intake passage bodies of the throttle devices disposed at the two points being connected to each other by at least one connecting member, the intake air amount control system further including bypass air passages mounted on opposed sides of the intake passage bodies forming a pair so as to extend around the throttle valves, respectively, air control valves mounted on the opposed sides of the intake passage bodies for controlling the opening degrees of the bypass air passages, respectively, and a synchronizing mechanism disposed between the pair of the throttle devices for synchronizing the operations of the air control valves.
With such arrangement, the bypass air passage is provided in the intake passage body of each of the throttle devices to extend around the throttle valve, and the amount of air flowing through the bypass air passage can be controlled by the air control valve. Therefore, the control of the small amount of air at the start of the engine can be carried out stably, whereby the idling rotational speed can be stabilized, as compared with the prior art in which the amount of air at the start of the engine is controlled by decreasing the opening degree of the throttle valve. In addition, the bypass air passages provided in the intake passage bodies and the air control valves mounted to the intake passage bodies are disposed on opposed sides of the intake passage bodies forming the pair. Therefore, it is possible to avoid an increase in size of the entire intake air amount control system, in spite of the provision of the bypass air passages and the air control valves. Moreover, since the synchronizing mechanism for synchronously operating the air control valves is disposed between the throttle devices forming the pair, the size of the entire intake air amount control system cannot be increased due to the provision of the synchronizing mechanism.
According to a second aspect and feature of the present invention, in addition to the first feature, the intake passage bodies forming the pair and having an identical shape, and the air control valves mounted to the intake passage bodies and having an identical shape are disposed symmetrically with respect to a center lying between both the intake passages and established on a straight line passing through axes of the intake passages in the intake passage bodies. With such arrangement, the preparation of a plurality of types of throttle devices is not needed, thereby enabling a reduction in cost and a simplification of the construction of the synchronizing mechanism.
According to a third aspect and feature of the present invention, in addition to the second feature, the connecting member is formed into a flat plate-shape. With such arrangement, the shape of the connecting member can be simplified, thereby providing a reduction in cost.
According to a fourth aspect and feature of the present invention, in addition to any of the first to third features, the synchronizing mechanism is supported on the connecting member. With such arrangement, an exclusive part for supporting the synchronizing mechanism is not required, whereby the number of parts can be reduced.
According to a fifth aspect and feature of the present invention, in addition to the second or third feature, the throttle passage bodies of the pair of throttle devices are disposed at a distance from each other in a direction parallel to the rotational axes of the throttle valves included in the throttle devices, and are connected to each other by a pair of the connecting members which form a substantially right-angled tetragon by cooperation with the intake passage bodies, and the synchronizing mechanism includes a first lever supported on an inner surface of one of the connecting members and connected to the air control valve of one of the throttle devices, a second lever supported on an inner surface of the other connecting member and connected to the air control valve of the other throttle device, and a synchronizing member disposed on a diagonal line of the substantially right-angled tetragon and connecting the first and second levers to each other. With such arrangement, sufficient strengths of the pair of throttle devices can be ensured and moreover, it is possible to protect the synchronizing mechanism by the connecting members and to simplify the synchronizing mechanism.
According to a sixth aspect and feature of the present invention, in addition to the first feature, a choke wire assembly is supported on the connecting member and connected to the synchronizing mechanism. With such arrangement, the structure of interconnection of the synchronizing mechanism and the choke wire assembly can be simplified, while increasing the degree of freedom of disposition of the choke wire assembly.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.